This invention relates generally to metallic particles and films, and more particularly to methods for their production by linking the electron pumping features of certain biological systems, such as the photosynthetic machinery, with the reductive precipitation of metallic particles.
Photosynthesis is the biological process that converts electromagnetic energy into chemical energy through light and dark reactions. In green algae and higher plants, photosynthesis occurs in specialized organelles, called chloroplasts. The chloroplast is enclosed by a double membrane and contains thylakoids, consisting of stacked membrane disks (called grana) and unstacked membrane disks (called stroma). The thylakoid membrane contains two key photosynthetic components, photosystem I and photosystem II, designated PSI and PSII, respectively, as depicted schematically in FIG. 1. During photosynthesis, water is split into molecular oxygen, protons and electrons by PSII. Electrons derived from the splitting of water molecules are transported through a series of carriers to PSI where they are further energized by a light-induced photochemical charge separation and transported across the thylakoid membrane where they are used for the enzymatic reduction of NADP.sup.+ to NADPH. This biological reaction is further utilized for chemical energy production, primarily in the form of ATP.
Ultrafine metallic particles, e.g., nanoparticles, are important precursors for use in the fabrication of advanced material structures, such as thin continuous films. Conventionally, metallic films have been deposited on substrates by methods such as chemical vapor deposition (CVD), sputtering, plating, and the like. Unfortunately, such methods do not generally offer a degree of control desired for the deposition of nanostructured materials, e.g., films having nanometer range thicknesses or grains. Therefore, a method which could drive the nucleation, growth and deposition of nanoparticles in a quantitative, rapid, and energy-efficient manner would be highly desirable for many applications, including materials processing, catalysis, separations, electronics, energy production processes, and environmental applications.
Despite the extensive investigation concerning the photosynthetic machinery, the use of photosynthesis-related principles for materials synthesis and processing has not been described. The present invention, by exploiting the electron pumping characteristics of the photosynthetic machinery for nanoparticle production and processing applications, provides improved methods and materials which overcome or at least reduce the effects of one or more of the aforementioned problems.